Repellent and reproductive inhibitory effects of Strychnos nuxvomica L. and Lepidium sativum L. against Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

In order to use eco friendly alternatives to chemical insecticides for the management of rice weevil Sitophilus oryzae L., hexane, ethyl acetate and methanol plant extracts from the leaves of Strychnos nuxvomica L., Lepidium sativum L. and Azadirachta indica A. Juss. were evaluated for repellent (area preference method) and reproductive inhibitory activities. Results showed that all the plant extracts were repellent at doses between 78.4 and 235.8 μg/cm² after 1, 6, 24, 48 and 72 h exposure. In repellency tests, hexane and ethyl acetate extracts of A. indica (>90.0%) followed by L. sativum (87.3%) were found to be the most effective compared to the extracts of S. nuxvomica at 235.8 μg/cm². In majority of the plant extracts, the per cent repellency increases from 6 to 24 h and then decreases gradually whereas in neem extracts the repellent activity exists even after 72 h. All the plant extracts significantly reduced F₁ progeny emergence compared to untreated control. At 7.5%w/w, ethyl acetate extract of S. nuxvomica (96.3%), and hexane extract of L. sativum (95.3%) effectively suppressed the F₁ progeny production followed by hexane and methanol extracts of A. indica (94.2%, 90.5%), respectively. The present work indicated that the plant extracts from Indian origin were potential grain protectants against S. oryzae.